Electroplating zinc



March 1941- L. R. WESTBR OOK 33, 00

' ELECTROPLATING zmc Filed Aug. 29, 1936 lzvrz-wroxa- A a/v A? 1 14-5759004 TTODA/EY Patented Mar. 4, 1941 PATENT, OFFICE-l ELECTBOPLATING ZINC Leon R. Westbrook, Cleveland Heights, Ohio, as- I slgnor, by mesne assignments, to E. I. du Pont de Nemours a Company, W

ilmington, Del., a

corporation of Delaware Application August 29, 1936, Serial No. 98,455

'16 Claims.

Thisinvention relates to the electrodeposition of zinc, and is particularly directed to processes and plating solutions wherein a bright, mirrorlike' zinc deposit is plated from a cyanide-zinc 5: bath which contains both an organic addition agent and a brightening metal. is further directed to the bright zinc deposits obtained, to the processes of obtaining such deposits from cyanide-zinc plating baths, and to processes and solutions employing an oxyheterocyclic compound and a brightening metal.

The electrodeposition of zinc, or electrogalvanizing, has been rather extensively employed because electro deposited zinc coatings, in addition to their low cost, display many characteristics which cause them to be particularly desirable as protective finishes. Zinc, being higher in the lectromotive series, will protect iron or steel against rust even after appreciable areas of the base metal are exposed, whereas the corrosion of iron or steel is accelerated by such metals as copper, nickel, and chromium. Despite their numerous advantages over many commonly used coating materials, electrodeposited zinc coatings have not enjoyed the use they deserve because ordinarily they do not possess and do not retain a pleasing appearance, and, consequently, for many purposes they are not acceptable.

Most'of the known methods of electrodepositing zinc result in dark colored or dull plates and,

'even when the deposits at first are fairly satisfactory, they may soon become dark and discolored.

-The poor appearance of most electrodeposited N zinc coatings has limited their use to protective applications, and those working in the art have,

for the most part. turned to other protective materials when it was desired to produce a finish of I pleasing appearance.

The electrodeposition of zinc has ordinarily w .beenaccomplished by the use of either an acidzinc bath or a cyanide-zinc bath. With neither of these baths has it been possible to obtain satisfactorily smooth and bright deposits, but the acid-zinc bath is more commonly used because :it leads to a brighter deposit with a better color than does the cyanide-zinc bath.

While, under favorable conditions, the deposits obtained from acid-zinc baths are relatively white, they are still none too satisfactory because of their'relatively coarse crystalline structure.

Numerous attempts have been made to improve the character of zinc deposits obtained from acid baths, and many addition agents, such as glycerine, dextrin, gum tragacanth,.licorice, naph- 5' thalene compounds, and aluminum compounds This invention have been used in conjunction therewith. While the use of addition agents improved the character of the deposits to some extent, the results were still none too satisfactory. I

In addition to the fact that acid-zinc baths do ;5 not produce satisfactory deposits, there are numerous other disadvantages attendant upon their use. For one thing, acid-zinc baths have very poor throwing power,and it is exceedingly diflicult satisfactorily to plate irregularly shaped objects. Another disadvantage of acid-zinc baths is their low cathode efliciency. As zinc is above hydrogen in the electromotive force series of metals, it is theoretically impossible to deposit zinc from acid solutions, but, of course, the rather great overvoltage of hydrogen does permit zinc deposition. Concurrently with the deposition of zinc, however, there is a very considerable evolution of hydrogen.

While the deposits obtained from cyanide-zinc 2 baths are poor in appearance, they'have a relatively flne crystalline structure. A few addition agents, suchas alum, gum arabic, and fluorides, have been tried in cyanide-zinc baths, but the results obtained were nonev too satisfactory. Aside from the poor appearance of deposits obtainable therefrom, cyanide-zinc baths have a number of advantageous characteristics. They have good throwing power, audit is therefore possible to deposit a relatively uniform zinc coating on irregularly shaped and recessed articles; Cyanide-zinc baths, moreover, have a relatively high cathode emciency which, of course, is very advantageous because the electric current applied to the bath is expended less upon the evolution of hydrogen, and. more upon the deposition of zinc.

Despite theadvantages of cyanide-zinc baths, they have not been much used by the an bea cause of the poor appearance of zinc deposits obtainable therefrom. Regardless of the disadvantages in operation of acid-zinc baths, they have been favored by those working in the art because of the somewhat better appearing deposits obtainable by their use.

A. number of proposals have recently been made for improved methods of electrodepositing zinc. The art has been enabled, using cyanidezinc baths, to produce relatively smooth and bright zinc plates. Such zinc plates, however, 50 require treatment in a bright-dip, such as dilutenitric acid, before they are entirely satisfactory for some pu poses. Those working in the art are frequently desirous of producing as even and bright a finish as possible, and, by using a brightdip, a zinc plate may be madebrighter and more uniform in appearance. The deposits, after bright-dipping, also display greater resistance to tarnishing and staining. I

The use of a bright-dip is illogical and uneconomical. The brightdip removes some of the zinc, and it is wasteful of time, materials, and.

labor to apply a zinc coating and then remove part of it. involves considerable expense for bright-dipping materials and labor. posited, therefore, in as bright a condition as possible so that a bright-dip treatment would be used, if at all, only when ,it is desiredto prolarly, are' of exceptional brightness and no dis-j cernible'efiect is produced by bright-dipping.

The baths of this invention have great throwing power and extremely xwide bright current density ranges and, unlike the baths of the prior art, they produce uniform zincc'oatings even on recessed articles. It is thereforeunnecessary to use bright-dips for the purpose, of making .the

coatings uniform. Also, by reason ofthe wide bright current density range displayed by cyanide-zinc baths of this invention, it is possible to plate at much higher current densities than have heretofore been feasible. I

'Employing the procedures of this invention, there are obtained even, lustrous zinc deposits directly from the plating bath, the deposits re-. quiri'ng no bright-dipping. The deposits are at least equal in appearance to the best brightdipped zinc deposits now being produced commercially and they are far better than most of the present commercial bright-dipped zinc deposits.

This invention, in its broader aspects, includes some baths which do not produce deposits of the highest brilliance, but which are, nontheless, a distinct improvement over the baths at present in commercial use. It may sometimes be sufilcient to produce deposits of moderate brightness, and, in any event, a bright-dip can be employed with results superiorto those of the prior art.

As is set forth in my co-pending application erial Number 14,589, filed April 4, 1935, a number of metals may advantageously be used to produce deposits of great smoothness and brightness. These metals appear to' exercise some synergetic action in conjunction with organic addition agents, and this action is particularly noticeable when the metals" are used in conjunction with oxyheterocyclic addition agents. Most of the orwheterocyclic compounds seem'to have only a small effectjwhen used in cyanide-zinc baths in the absence of a brightening metal. As will be noted later, however, heterocyclic compounds may sometimes be used alone for the benefit which they do offer.

Oxyheterocyclic compounds, typical of which are furfuralderivatives, coumarin, pyronine, and pip r-opal, are, of course, characterized by the The bright-.fdip treatment, moreovenf- The zinc should be de- The deposits produced acpresence of an oxy 'eterocyclic ring, and it is be lieved that it is this characteristic which determines the suitability of compounds for my purposes. An oxyheterocyclic ring is, of course, a cyclic ring of carbomand oxygen atoms.

- The oxyheterocyclic addition agents employed should be relatively stable in the bath. That is, they should not lose their oxyheterocyclic form upon contactiwith a cyanidezinc plating solution. The compounds, moreover, should be at .least slightly soluble in a cyanide plating bath. The addition agents suitable for use with brightening metals in accordancew'lth this invention -wlll.be discussed in greater detail in the examples given hereinafter. The brightening metals to be used in conjunction' with oxyheterocyclic compounds according to this invention include aluminum, titanium, and metals found in sub-groupl of groups VI and VII, and-'in group VIII series 4 of Mendelyeevs periodic arrangement of the elements. Most of these 'metals themselves exercise a profound effect upon thecharacter of zinc electrodeposits obtained from cyanide-zinc plating baths, and,

when used with oxyheterocyclic compounds, they cause the formation of zinc deposits of great brilliance and beauty. u I

Molybdenum is by far the guest satisfactory of the brightening metals .for use with oxyheterocyclic compounds, the deposits obtainable by the use of such a combination being markedlysuperior to those obtainable with most other'combinations disclosed herein.

Thebrightening metals, molybdenum, chromium, tungsten, and uranium found in group VI sub-group 1, may be addedto a cyanidezinc bath in the form of a niolybdate, chromate, tungstat, or uranate of sodium or potassium, or other such compounds which are soluble inthe bath. The metals of group VlI sub-group 1, manganese and rhenium simllarly, should be added in the form of soluble compounds. Aluminum may be added as aluminum sulfate, and titanium may be added as titanyl sulfate. a

The metals of group VIII series 4 0i' the periodic system have little eifect upon the character of a' zinc electrodeposit when used alone but, in com-' mon with the other brightening metals, they ex-, 4

ercise a synergetic action with oxyheterocyclic compounds. The metals of group VIII-series '4 are also advantageously employed by reason of their effect upon the metals of sub-group Iof groups VI and VII. These metals may be added to the bath in the form of such alkali or cyanide soluble compounds as potassium ferrocyanide, co-

balt sulfate, nickel sulfate, cobalt oxide, and nickel oxide. v

The combination of an oxyheterocyclic compound and a brightening metal is employed in a cyanide-zinc bath, numerous examples of which will be given hereinafter. While the cyanide-zinc baths shown herein are typical, it will be understood that the principles of my invention are applicable to any cyanide-zinc plating bath. To obtain the best results it is desirable that the cyanide-zinc plating bath be as pure as possible, and it is particularly important that lead compounds be absent.

zinc deposits are ordinarily examined visually and described loosely as "rough," treed," smooth, or bright. tions are diiferently used by difierent observers, and it is virtually impossible to compare zinc deposits obtained at different times or made by different individuals.

These inexact designa- So that electrodeposited zinc-coatings could be more accurately described, an instrument was designed to measure the amount of light reflected by the coatings. This reflectometer, shown in the drawing, is similar to instruments heretofore used for the study of enameled surfaces, paint films, and the like. p

In the drawing, I designates a box having a cover 2 and divided by a central partition I. In one side of the box there is provided a light source 3, a fifty candlepower automobile headlight bulb. To furnish current to the bulb, a storage battery is used, the current being regulated by the use of a rheostat so that about three volts are supplied to the lamp. l

Below the bulb there is provided a concave mirror 4 which serves to intensifythe light to some extent. This concave mirror is about three inches below the bulb.

Above the light bulb there is a black partition 5 provided with a one-half inch slit. The bulb is about threeand one-half inches from the specimen being tested.

Light from the bulb I passes thru the slit 6 and is reflected by the specimen to the selenium photoelectric cell 8. The photoelectric cell is on a slight incline, being supported by the member 8. The cell is about five and one-half inches from the specimen.

The photoelectric cell is connected to a microammeter III which shows directly the number of microamperes generated by the cell in response to the light reflected by the specimen.

The top .2 of the box I has a slit H therein thru which light can pass. A metal plate I2 is set over the hole, the plate having a one-quarter by three-quarter inch rectangular slit. On top of the box and covering the metal plate there is positioned a chamois skin ll upon which specimen plates may be placed with'out danger of scratching. 'I'hechamois is provided with an opening registering with the slit l3.

Before starting to use the refiectometer, it was calibrated with a standard reflecting surface. A silverv mirror was made by plating a polished copper sheet with silver and then bufllng. The mirror was placed face down on the chamois over the slit. The current supplied to the bulb 3 was then adjusted until the micro-ammeter read 49.

. In view of the fact that a silver mirror quickly loses its maximum brilliance, and in view of the diillculty' of preparing new silver mirrors, a less changeablesecondary standard was established.

A silvered glass mirror was placed face down depending upon its temperature and upon other variables. At frequent intervals a new polished silver mirror was prepared in accordance with the best practice and used to recheck the glass mirror so that when the silver mirror read 49 microamperes, a portion of the glass mirror reading 45 microamperes would be used as standard. c

When no specimen is placed on top of the reflectometer, a reading of less than one microampere is obtained. This reading represents the error by reason of light leaking to the photoelectric cell.

In the following examples, unless otherwise stated, specimens were plated on polished copper sheets at current densities from flve to one hundred and fifty amperes per square foot. Specimens plated at current densities of about seven, twenty-five, forty, and eighty amperes per square foot were placed on the reflectometer for brightness determinations.

So that the results would be comparable, the deposits were made on copper plates polished so that on the refiectometer,- readings of to would be obtained over the whole surface.

When plates differing as much as 5 microamperes were zinc plated under the same conditions and from the same bath, the zinc deposits diifered by only about one microampere or less.

While most commercial zinc plating is not done on polished surfaces, the deposits obtained on polished copper sheets are nonetheless signiflcant. A bath which produces a dull deposit on a polished surface will produce a dull and poor deposit on a matte surface, while a bath which produces a bright deposit on a polished surface will produce a correspondingly better deposit on a matte surface. The deposit obtained on polished sheets are therefore valuable in indicating, which of a number of baths would lead to the brightest deposits when applied to ordinary commercial work.

In the following examples, unless otherwise stated, a cyanide-zinc bath of the following composition was used:

Grams per liter Zinc cyanide (Zn(CN) z) 60 Sodium hydroxide (NaOH) '18 Sodium cyanide (NaCN) 42 Example 1 The oxyheterocyclic compound piperonal is a colorless crystalline material sparingly soluble in water and in cyanide-zinc plating baths. The compound is also known as heliotropin and as 3,4-methylenedioxybenzaldehyde, and it is characterized by an intense heliotrope-like odor.

A cyanide-zinc plating bath was made up according to the above standard m thod, and there was added thereto:

Grams per liter' Molybdenum trioxide (M603); 8.0 Piperonal 3.5

Znc was'deposited on a number of polished copper sheets, and its brightness determined on the reflectometer according to the above discussed methods. The results at the current densities indicated were as follows:

Current density (amps. per sq.

ft.) Not bright-dipped 33 38 38 30 Bright-dipped 3'7 38 40 36 'The deposits were extremely brilliant and they reflected images with mirror-like fidelity when visually observed. While the reflectometer shows a considerable difference between bright-dipped and unbright-dipped plates, it is notedthat when zinc plated sheets were bright-dippedfor about one-half of their area, very little difference.

could be observedwisually. In some instances it was possible to discern a line where the'brightdipped and unbright-dipped portions 'met, but

on several deposits no such line could be distinguished. I

A plate, part 'of which had been bright-dipped, was subjected to a corrosive atmosphere which ordinaril tarnishes unbri ght-dipped platings in .a few hours, and'after six days the upbrightdipped portion appeared as bright as the portion which had been bright-dipped.

A large number'of commercial steel articles of various kinds were plated in various types of insmaller amounts may be employed with good results. At one gram per liter, for instance, the

results were not substantially different from those obtained with the bath given above. I I

The piperonal does not deteriorate in the bath as do certain oxyheterocyclic addition agents: mentioned hereinafter. It is interesting to note that the presence 'of piperonal in a bath such as the one of this example seems-to increase Zinc cyanide (Zn(CN)z) 60 Sodium cyanide (NaCN); 23 Sodium hydroxide (NaOH) 53 slightly the content of molybdenum in the deposit, o

For purposes of comparison, an electroplating bath of theprior art was examined according to the methods given herein. The bath selected is a very excellent one described in the second editionof Blum and Hogabooms Principles of Electroplating on page 331; formula No. l. Thi

. bath was made-up as follows:

Grams per liter A number of specimen plates were made according to the above described procedure and the brilliance determined on the reflectometer with the following results:

Current density (amps. per sq.

ft.) 7 25 40 80 Not bright-dipped 12 15 4 9 Bright-dipped 29 29 18 27 It will be observed that without a bright-dipping treatment the plate obtained was exceedingly dull. The use of a bright-dip effected a very great improvement in the deposit, tho even after brightdipping the deposit was not as bright as those obtained according. to this example even without a bright-dipping treatment.

The cyanide-zinc plating bath used as standard in this application was made up without the use of addition agents, and a number of deposits made therewith. The following brightness read- 1112s were obtained: I A II Current density. (amps. per sq.

ft.) '1 Not brightedipped 15 15 4 f1 Bright-dipped-... 30 30 19 11 A cyanide-zinc plating bath was madeupusing 3.5 grams per liter of .piperonal but omitting molybdenum. Zinc electro-deposits' obtained 25 to so".

from this'bath gave the following brilliance read-' ings: I Current density. (amps. per sq. ft. ;I I Not bright-dipped 25 11 8 10 Bright-dipped '36 29 27 26 It will be observed th'at piperonal 'aloneeflects some improvement time deposits, tho the deposits, before bright-dipping particularly, are still rather dull;

' readings were obtained on deposits produced in this bath: I Current density (amps. per sq. I

it.) 'l .25 40180 Not bright-dippetL ep15 22, 30 30 Bright-dipped' 28 30 33 30 From the above it win be apparent that the use of a combination of piperonal and molybdenum results in zinc deposits of much greater brightness and uniformity than would be expected. I

' believe that there is a synergetic action between the organic addition agent and the metal brightener, each being influenced by the other, and both cooperating to produce deposits of unexpected character.

' Examples I A cyanide-zinc plating bath was .madeup using piperonal with another brightening metal. To the standard cyanide-zinc bath above given, there was added: I

Grams per-liter Chromium sulfate (cmsom-ismo) 4.0 Piperonal e 3.5

A number of zinc deposits were produced using this bath, and the following reflectometer read ings obtained:

Current density--- i '1 25 80 Not bright-dipped 34 34 32" 30 Bright-dipped 38 34 31 30 The deposits obtained had a. very excellent and brilliant appearance, and to the eye 'they'appeared even brighter than the'deposits obtained in Example 1.

Unfortunately, the chromium slowly precipitates from the solution, and for this reason is not as desirable a metal brightener asrmolybdenum. The metal content of the bath can, of course, be maintained by adding chromiumsulfateto-replace the chromium which leaves the solution.

To observe the effect of the metal brightener apart from the organic addition, a bath-was made up as above but omitting the piperonal. The reflectometer readings on plates madewith this bath were:

Current density 7 25 40' so aasasoo Example 3 A cyanide-zinc bath employing two metal brighteners in addition to an oxyheterocyclic compound was made up as follows:

Grams per liter Zinc oxide (ZnO) 45. sodium'hydroxlde (NaOH) 38. Sodium cyanide (NaCN) 100. Molybdenum trioxide (MoOa) 3. Manganese-cyanide 2.5 Piperona 3.

The bath was made up with very pure zinc oxide, sodium hydroxide, and sodium cyanide, and electrolytic zinc anodes were employed to avoid the responds to about two grams per liter of molyb-,

denum.

Excellent results were obtained using this bath. The zinc deposits were very bright, particularly after bright-dipping. The reilectometer readings taken on specimens made at the indicated current densities were as follows:

Current density 'l 25 40 80 Not bright-dipped 35 36 38 32 Bright-dipped 40 41 39 33 Example 4 A cyanide-zinc plating bath employing a combination of metals of Group VI sub-group 1, Group VII sub-group 1, and Group VII series 4 was made up as follows: r

Grams per liter Zinc oxide (ZnO) 45 Sodium hydroxide (NaH) s.. 38 Sodium cyanide (NaCN) I00 Manganese-cyanide 10 I Potassium ferrocyanide (K4Fe(CN) c.3HaO) Molybdenum trioxlde (M003) 4 Piperonal 3 1 Zinc deposits made from the bath of this example were of about the same appearance regardless of current density. Irregularly shaped objects, accordingly, were given a coating of very uniform appearance by the use of this bath. The reflectometer readings were as follows:

Current density -i "I 25 40 80 Not bright-dipped 33 35 35 35 Bright-dipped; 38 38 38 38 Example 5 A cyanide-zinc bath employing a metal of Group VIII series 4 as well as an oxyheterocyclic compound was made up with:

Grams per liter Cobalt sulfate (COSO4.7H2O) 8. Piperonal 3.5

At current densities up to about forty amperes per square foot very good results were obtained using this bath. The reflectometer readings at the current densities indicated were:

Current density 7 25 40 80 Not bright-dipped 34 32 7 12 Bright-dipped 39 37 15 24.

The cobalt sulfate used corresponds to about one and twenty eight hundredths of a gram per liter of cobalt. Very similar results were obtained using sixty four hundredths of a gram per liter of cobalt, or about four grams per liter of cobalt sulfate.

To observe the effect of the metal brightener apart from the organic addition, a bath was made up as above but omitting the piperonal.- The reflector readin s on plates made with this bath were: p

Current density l 7 25 40 80 Not bright-dipped"; 10 23 23 '1 Bright-dipped '24 33 34 23 Example 6 x A cyanide-zinc bath employing a metallic brightening agent from Group VII sub-group 1 in conjunction with an oxyheterocyclic compound was made up as follows:

. 1 Grams per liter Zinc oxide (ZnO) 45.

Sodium hydroxide (NaOH) 88. Sodium cyanide (NaCN) 100.. Manganese sulfate (MnSOsAHaO) 1. Piperonal i 3.5

The manganese sulfate corresponds to about twenty-five hundredths of a gram per liter of manganese. Both the piperonal and the manganese sulfate were used in about the maximum amount soluble in the bath. 'More manganese sulfate was added to the bath in various tests without appreciably different results being obtained. Excellent results were obtained using the bath of this example, and the following reflectometer readings were noted:

Current density -l 7 25 80 Not bright-dipped 29 30 10 2 Bright-dipped 40 34 18 -6 It is noted that the deposits were somewhat cloudy before bright-dipping, therefore causing the reflectometer readings to be rather unexpectedly low. After bright-dipping, however, the deposits .were quite brilliant and of very good character.

To observe the effect of the metal brightener apart from the organic addition, a bath was made up as above but omitting the piperonal. The reflectometer readings on plates made with this bath were:

Current density Not bright-dipped 18 13 3 2 Bright-dipped 31 27 5 2 Example 7 A cyanide-zinc bath using another metal of Group VIJI series 4 in conjunction with piperonal was made up with:

Grams per liter Nicke1 sulfate (NiSOflHaO) 0.5 Piperonal 3.5

Using this bath, some deposits of pleasing appearance where obtained. The deposits were somewhat white in color and probably for this reasonthe reflectometer readings were not as high as one would expect from visual examination. The reflectometer readings were as follows:

Current density 7 25 40 80 Not bright-dipped 30 29 30 12 Bright-dipped 31 28 27 12 Bright-dipping the plates was not very successful because the bright-dip treatment caused the deposit to become dark and streaked.

To observe the eifect of the metal brightener apart from the organic addition. a bath was made up as above but omitting the piperonal. The refiectometer readings on plates made with this bath were:

Current density 7 25 40 so Not bright-dipped 31 10 24 23 Bright-dipped 29 16 22 24 Example 8 A cyanide-zinc bath was made up with:

Grams per liter Potassium ferrocyanide (K4Fe(CN) e3H2O)- 12. Piperonal 3.5

Zinc deposits obtained using this bath had a brownish film. Reflectometer readings were obtained as follows:

Current density 7 25 40 Not bright-dipped 23 14 14 14 Bright-dipped 1 3'7 35 35 '35 It will be observed that bright-dipping'the plates removed the film andled to the production of very satisfactory deposits.

To observe the efiect of the metal brightener apart from the organic addition, a bath was made up as above omitting the piperonal. The refiectometer readings on plates made with this bath were: I

Current density n 7 25 40 80 Not bright-dipped- 13 12 9 9 Bright-dipped. 23 ,27 26 27 Example!) A cyanide-zine plating bath was made up with:

. e Grams per liter Titanyl sulfate (TiOSOl) 0.5 Piperona 3.5

Employing this bath, specimens were obtained with the following reflectometer readings:-

Current density f7 25 40 30v Not bright-dipped 27 24 13 7 Bright-dipped 34 32 28 30 These deposits were dull by reason of a film thereon which bright-dipping removed.

To observe the effect of the metal brightener apart from the organic addition, a bath was made up as'above but omitting the piperonal.

The refleetometer readings on plates made with this bath were: v

Current density 7 25 40 80 Not bright-dipped 16 14 11 13 Bright-dipped. 33 29 25 27 Example 10 A cyanide-zinc plating bath was made up with:

1 Gramsperliter Potassium perrhenate (KReOO 0.1 Piperonal 3.5

Deposits produced at the indicated current densities gave the following reflectometer readings:

Current density 7 25 40 80 Not bright-dipped 22 21 27 24 Bright-dipped .2 32 29 35 36 To observe the effect of the metal brightener apart from the organic addition, a bath was made up as above but omitting the piperonal.

" the o wing results were obtained p The reflectometer readings on plates made with this bath were:

Current density .j Not bright-dipped 24 24 22 5 Bright-dipped 30 23 27 14 5 Example 11 A cyanide-zinc plating bath was made up as follows: I

- Grams per liter Zinc oxide (ZnO) '45. Sodium hydroxide (NaOH) 38. Sodium cyanide (NaCN) e 100. Tungsten trioxide (WOa) 8. Piperonal 3.5

The tungsten trioxide used corresponds to about six and four-tenths grams per liter of tungsten. Specimen plates were made up at the below indicated current densities with the following resuits:

Current densit u"; "l' 25 40 so Not bright-dipped 32 33 13] 4 Bright-dipped. 38 36 1'7 8 25 Example 12 35 Another oxyheterocyclic compound which may advantageously be employed is piperonylic acid. This compound, also known as methylene protocatechuic acid, maybe regarded as a. derivative of piperonal. Like piperonal, piperonylic acid is characterized by the presence of the methylenedioxyphenyl group. A cyanide-zinc plating bath was made 'up with:

' Grams per liter Molybdic acid 8 Piperonylic acid 4 The piperonylic acid went into solution rather readily. A number of polished copper sheets were zinc plated using this bath, andthe following reflectometer readings were obtained at the indicated current densities:

Current density 7 25 40 80 Not bright-dipped 17 36 36 29 Bright-dipped 33 40 37 30 A cyanide-zinc plating bath was also made up as above using piperonylic acid but omitting the molybdic acid. When not using the metal bright- Current density '1 25. 4o so Not bright-dipped. 18 iv 16 11 Bright-dipped 30 33 30 21 Example 13 A cyanide-zinc plating bath was made up with:

' Grams per liter 70 Aluminum sulfate (Alz(504)s) 12 Piperonylic acid a 5 The deposits obtained using this bath were of very good character tho'the reflectometer readings were somewhat low before bright-dipping. 75

Current density '1 25 40 so Not bright-dipped 24 21 23 23 Bright-dipped 41 84 '32 A cyanide-zinc plating bath was made up as above but omitting the organic addition agent piperonylic acid. With aluminum thus used as a metal brightener, the following results were obtained:

Current density 7 25 80 Not bright-dipped 6 8 3 2 Bright-dipped 14 16 11 7 Example 14 v A cyanide-zinc plating bath was made up with:

v Grams per liter Chromium sulfate (Cr1(SO4):-15H:O) 4 Piperonylic acid 4 Employing this bath, the following results obtained:

Current density 'l 25 40 80 were Not bright-dipped. so 33 26 24 Bright-dipped A. so 32 2s 26 Example 15 A cyanide-r .nc plating bath was made up with:

Grams per liter Cobalt sulfate (00301-71110) 8 Another oxyheterocyclic compound closely allied to piperonal is piperine. This compound is characterized by the presence of the methylene dioxyphenyl group. Piperine is only slightly soluble in water, and in the following examples it was added to the cyanide-zinc baths in alcohol solution. A bath employing this oxyheterocyclic compound together with my preferred met brightener was madeup with: g i

Grams per liter Molybdenum trioxide (M003) s Piperine 1 using the bath of this example gave the following reflectometer readings at the indicated current densities.

Current density; '1 25 40 so Not bright-dipped"; 17 22 27 24 Bright-dipped 32 32 so 26 A bath similar to that of this examplewas made -up using piperine but omitting molybdenum.

The following results were obtained:

Currentdensity a 25 40 so Not bright-dipped 1'1 7 '1 c Bright-dipped. 32 21 21 1s Example 17 A cyanide-zinc bath was made up with:

' Grams per liter Chromium sulfate (6118001451120) 4 Piperine 1 Using this bath, the following results were obtained: Y

Current density 'l 25 40 Not bright-dipped 30 27 28 28 Bright-dipped 37 32 31 28 I Example 18 A cyanidezinc plating bath was made up with:

' Grams per liter Nickel ammonium sulfate v (NiBOdNHshSOs-BHsO) 1 Piperine 1 Plates made using this both were quite satisfactory without bright-dipping and. as is usual with deposits made employing nickel, bright-dipping was not advantageous. The reflectometer readings at the current densities indicated .were as follows:

Bright-dipped 2a 35 31 23 Example 20 Safrole, the oxyheterocyclic compound from which plperonal is commercially derived, is also Current density v. '1 25 '40 so I Not bright-dipped--- 35 36 34 23 Bright-dipped 35 3a 2a 15 Example 19 V v A cyanide-zinc plating bath was made up with:

. Grams per liter Cobaltsulfate. (00804-71120) 8 Pipe 1 Employing this bath the following results werev obtained: Current density 7 25 40 so Not bright-dipped 17 2'! 25 17 characterized by the presence of a methylenedioxyphenyl group. Safrole is quite insoluble in water, and even adding it to the bath in alcohol solution does not greatly increase the. amount of safrole which can be dissolved. Despite the almost negligible solubility of this compound, baths employing it show a very considerable improvement. Employingthis oxyheterocyclic compound and applicant's preferred metal brightener, a cyanide-zinc plating bath was made up with:

Deposits of good appearance were obtained using Grams per liter Molybdenum trioxide (M003) 8 safrole 1 this bath. The reflectometer readings were as' follows at the indicated current densities:

Current density 'l 25 40 80 Not bright-dipped 13 25 28 27 Bright-dipped 27 34 35 34 g Current density "L- 7 25 40 so Not bright-dipped 12 10 9 8 Bright-dipped 30 29' 28 2 8 Eaample 21 v A cyanide-zinc bath was made up with:

- Grams per liter Chromium sulfate (Cr(SO4)a-15H20 4 Safr v 1 Employing this bath, the following results were obtained;

Current density Not bright-dipped. 21 23 23 22 Bright-dipped 28 29 29 32 Ezrample 22 I A cyanide-zinc plating bath was made up with;

. j Grams per liter Cobalt sulfate (CoSOr'll-IzO) 8 Safr e l The following reflectometer readings were obtained at the indicated current densities:

Current density 'l 25- 40 80 Not bright-dippedhu 23 27 Bright-dippedm n'. l-. 26 31 31 31 Example 23 Another oxyheterocyclic compound characterized-by the presence of the methylenedioxyphenyl group is piperonyl alcohol. This compound was employed together with a metal brightener in a cyanide-zinc plating hath made up including:

, Grams per liter I Molybdenum trioxide (M0O3)' 8 Piperonyl alcohol 5 Current density; n 25 40 so Not bright-dipped 13 14 10 11 Bright-dipped 27 30 30 30 Example 24 Another oxyheterocycliccompound related to piperonal and characterized by the presence of the methylenedioxyphenyl group is piperonal acetophenone. This compound was employed in conjunction 'with a metal brightener in a bath made up with:

A Grams per liter Molybdenum trioxide (M003) 8 Piperonal acetophenone 1 2 The piperonal acetophenonewas quite insoluble,

tho the small amount which dissolved efiected considerable improvement. Employing this bath the following reflectometer readings were obtained at the indicated current densities:

Current density 7 25 40 80 Not bright-dipped 16 29 34 28 Bright-dipped s 33 36 31 A similar cyanide-zinc bath was made up employing piperdnal acetophenone but omitting molybdenum. The following results were ob tained:

Current density. '1 25 so Not bright-dipped -15 2s 25 21 Bright-dipped 28 so 33 as Example 25.

. namic lactone.l Employing-'coumarima cyanide zinc bath was made up fiS'fOllOWSl. I

-.r v Gramsperliter Zinc cyanide (Zn(CN)2) 60. Sodium hydroxide (NaOH) 80. Sodium cyanide (NaCN) 40. Molybdenum trioxide (M003) 8.4 Coumarin 3.

Current density '7 2.5 40 80 Not bright-dipped 30 32 35 26 Bright-dipped 32 35 34 35 When the bath of this example-was used to plate 30 work of commercial character, zinc deposits of excellent appearance were obtained. Bright-dipping the plated articles effected no discernible change in the appearance of the deposits.

Using the bath of this example, deeply. recessed 35 articles were coated with a zinc deposit of uniform appearance. Brilliant deposits were obtained from current densities of from about three to about one hundred and fifty amperes per square foot. The bath was operated for several 40 days and. unlike some of the baths hereinafter described; it appeared to be quite stable.

The coumarin may be used in varying amounts in the bath, of course, the amounts used in this example being about optimumL. This concentra- 4 tion is about the upper limit of the solubility of coumarin in the bath used. Smaller amounts of coumarin may advantageously be employed and results which were not greatly difierent were obtained when one gram per liter of coumarin was used in a bath of the samecomposition. Even smaller amounts of coumarin exercise a beneilcial eflect, the in general itis preferable to use about one gram per liter or more.

A bath was made up as above using coumarin but omitting the molybdenum. The following results were obtained:

Current density '1 25 40 so Not bright-dipped 14 14 11 11 Bright-dipped so 30 24 23 Example 26 A cyanide-zinc bath --employing two met brighteners in addition to the oxyheterocylic compound was made up as follows:

. Grams per liter Zinc oxide (ZnO) 45. Sodium hydroxide (NaOI-IL'. '38. Sodium cyanide (NaCN) 100. Molybdenum trioxide (M003) 3. Manganese-cyanide 2.5

Coumarin 3.

The bath was made up with very pure zinc oxide. sodium hydroxide, and sodium cyanide, and electrolytic zinc anodes were employed to avoid the introduction of deleterious impurities into the. bath. The manganese was-added to the bath in the form of a manganese-cyanide complex which was precipitated from a water solution of manganese sulfate by adding thereto a water solution of sodium cyanide. The amount of manganese cyanide used is equivalent to about twentiflve I Example 27 A cyanide-zinc bath containing a metallic brightening agent from group VII sub-group 1 as well as an oxyheterocylic compound was made up as follows:

Grams per liter Zinc oxide (ZnO) 5 Sodium hydroxide (NaOH) 38 Sodium cyanide (NaCN) 80 Manganese sulfate (MnSOuiI-hO) 1 C'oumarin 3 A number of deposits were made using this bath and it was found that the bath has a more restricted bright range than does the bath of the preceding example. -At a current density of about twenty-five amperes per square foot, an unbright-dipped plate had a reflectometer reading of twenty-one and a bright-dipped plate a reading of thirty-four. Manganese sulfate was also used to the amount of fifteen grams per liter in a bath such as that of this example without greatly different results being obtained.

Example 28 I A cyanide-zinc plating bath similar to tho of the above examples but containing a metal brightener of group VI sub-group l was made up as follows:

. Grams per liter Zinc oxide (ZnO) Sodium hydroxide (NaOH) 38 Sodium cyanide (NaCN) 100 Tungsten trioxide (WQa) 5 Coumarin 3 The tungsten trioxide corresponds to about four grams per liter of tungsten. Polished plates and commercial articles were given a zinc electrodeposit using this bath with excellent results. 6 On a polished copper plate at a current density of twenty-five amperes per square foot, an unbright-dipped deposit gave a reflectometer reading of seventeen, and a bright-dipped deposit a reading of thirty-two.

Example 29 A cyanide-zinc bath using a metal brlghtener from group VIII series 4 together with an oxyheterocyclic compound was made up as follows:

Grams per liter Zinc oxide (ZnO) 45 Sodium hydroxide (NaOH) 38 Sodium cyanide (NaCN) 110 Cobalt sulfate (C0SO4.7H2O) 12 Covumarim 3 The cobalt sulfate used corresponds to about two and fifty-two hundredths of a gram of cobalt per liter. This bath had a rather restricted bright range, the deposit being brightest at current densities from about thirty to about sixty amperes per square foot. At about forty amperes per square foot, an unbright-dipped plate gave a reflectometer reading of about twenty-five, and a bright-dipped plate gave a reading of thirty-four.

- A cyanide-zinc plating bath was made up as above but using three grams per liter of cobalt sulfate. Very similar results were obtained using this bath, tho they were not quite as good as the results obtained with the bath above given. I

Example 30 A cyanide-zinc bath employing brightening metals of group VI sub-group, group VJI subgroup 1, and group VIII series 4, as well as an oxyheterocyclic compound was made up as follows:

I ,Grams per liter Zinc oxide (ZnO) 45' Sodium hyroxide (NaOH) Sodium cyanide (NaCN) 100 Manganese-cy ni 10 Potassium ferrocyanide (K4Fe(CN) c.3H20) 5 Molybdenum trioxide (M003) .2. 4 Coumarin 3 The molybdenum trioxide used corresponds to about two and seven tenths grams per liter of molybdenum, the potassium ferrocyanide corresponds to about sixty-six hundredths of a gram per liter of iron, and the manganese-cyanide, a complex prepared as in Example 26, corresponds to about one gram per liter of manganese. It is observed that the iron compound exercises a solubilizing effect on the manganese compound.

At a current density of about seven amperes per square foot an unbright-dipped deposit gave a reflectometer reading of thirty-two, and a brightdipped deposit at the same current density gave a reading of thirty-seven.

Example 31 A cyanide-zinc plating bath was made up with:

v Grams per liter Chromium sulfate (cr(som.15rno) 4 Coumarin 3 His noted that the chromium sulfate did not entirely dissolve in the bath. Usingthis bath ,for zinc plating a number of polished copper sheets, the following reflectometer readings were obtained at the indicated current densities:

Current density 7 25 40 Not bright-dipped 24 22 20 16 Bright-dipped 32 27 23 23 Example 32 x A cyanide-zinc plating bath was made up with:

I Grams per liter Nickel sulfate (NlSO4.7H2O) 0.5 Coumarin 3.

Employing the bath of this example the following results were obtained:'

Current density '7 25 40 80 Not bright-dipped 19 20 32 31 Bright-dipped 19 25 30 28 It will be noted that, as is usual with baths containing nickel as a brlghtener, the action of a bright-dip was quite erratic. At a current denthe bright-dip was even more injurious.

Ezample 33 A cyanide-zinc plating bath was made up with:

- Grams per liter Molybdenum trioxide (M003) 8 Furfural 6 It is observed that the molybdenum trioxide used corresponds to about five and four-tenths grams per liter of molybdenum. Using this bath immediately after it was made up, a number of polished copper plates were given a coating of zinc at current densities from about three to about one hundred and fifty amperes per square foot. Over this wide range of current densities the zinc deposits were brilliant and lustrous, re-' fleeting images with mirror-like fidelity when observed visually. sheets were bright-dipped over a portion of their area, and when these partially dipped plates were visually observed it was barely possible to discern a line of demarcation between the brightdipped and the unbright-dipped portions. The following reflectometer readings were obtained with deposits made at the indicated current densities:

Current density 7 40 so Not bright-dipped 20 34 33 33 Bright-dipped 28 36 36 35 The bath of this example was also used shortly after it was prepared .to plate a number of steel stampings. The deposits obtained directly from the bath were excellent in appearance 'and, apparently, were'in every respect equal to deposits obtained after bright-dipping.

While the use of furfural in conjunction with 'molybdenum leads to exceptionally good results when the bath is fresh, after a short time the bath deteriorates becoming less and less satisfactory. Not only does the effectiveness of the furfural seem to diminish, but some action appears to occur which results in a poisoning of the solution. The addition of more furfural does not revivify the bath. Furfural, then, can only be used to produce very brilliant deposits for a relatively short time.

If, after a bath such as that shown in this example becomes poor, it is desired to improve its characteristics, this may be done .by allowing thebath to-pass slowly thru a column of zinc turnings, after-which an amount of furfural equivalent to that originally used may be added. By repeated reviviflcation and addition of furfural, the bath may bev made to operate continuously, but this is a relatively troublesome and expensive procedure and would not ordinarily be resorted to unless some particular circumstances ofier justification.

It is to be observed that while furfural is used at about an optimum concentration in this example, the amount employed may be widely varied. It is generally desirable to use from about two grams per liter to about five grams per liter of furfural in baths of the type of this example.

A bath was made up using furi'ural as above, but omitting the molybdenum. With this bath Deposits made on copper the following re ectometer readings were obtained at the indicated current densities:

Current density 7 25 40 80 Not bright-dipped 22 25 31 31 Bright-dipped 34 32 33 Example 34 A cyanide-zinc plating bath was made up with: r

, I Grams per liter Nickel sulfate. (msommo) 0.5

Furfurad 6.

Good deposits were obtained using this bath, but a bright-dip should not be used on this type of deposit because of the fact that nickel was used as the metal brightener. The following reflectometer readings were obtained at the indicated current densities:

Current density 'z 25 40 so Not bright-dipped 32 32 31 29 Bright-dipped 2o 24 23 1'1 Example 35 Another oxyheterocyclic compound which may be used with metallic brighteners according to my invention is furfuran. This oxyheterocyclic compound may be considered a furfural' derivative which contains the characteristic oxyheterocyclic ring of four carbon atoms and one oxygen atom.

A cyanide-zinc plating bath was made up with: 6mm per liter Molybdenum trioxide (M003) 8 Furfuran 5 Excellent zinc deposits were obtained using this bath. The following refiectometer readings'were taken at the indicated current densitiesz Current density 7 25 40 so Not bright-dipped"; 1'6 28 29 26 Bright-dipped 25 32 35 so furan but omitting molybdenum. The following reflectonieter readings were obtained on deposits made at the indicated currentdensities:

Current density; 7 25 40 80 Not bright-dipped 11 16 21 23 Bright-dipped 23 28 34' 33 Example 36 Zinc oxide (ZnO) Sodium hydroxide (NaOH) 38. Sodium cyanide (NaCN) 80 Manganese sulfate (MnSO4-4HaO) 15 Furfuran 7 The manganese sulfate employed corresponds to about three and seven-tenths grams per liter of manganese. Zinc deposits were made on polished copper sheets, and at a current density of about seven amperes per square foot an unbright-dipped deposit gave a refiectometer reading of twenty four, and a bright-dipped deposit gave a reading of thirty three.

Emmple 37 A cyanide-zinc plating bath was made up with:

. Grams per liter Cobalt sulfate (CoSO4-7H2O) 8 Furfuran 5 Employing this bath, deposits with the following characteristics were obtained at the indicated current densities:

Current density 7 40 so Another oxyheterocyclic compound which may be used as an addition agent according to my invention is pyronine. A cyanide-zinc plating bath was made up with:

Grams per liter Molybdenum trioxide (M003) 8 Pyronine 5 This bath was employed to zinc plate a number of polished copper sheets and a number of commercial steel articles. The zinc deposit on the polished copper sheets was brilliant and lustrous, and reflected images with a mirror-like fidelity when visually observed. Zinc deposits made at the indicated current densities gave the following reflectometer readings:

Current density 7 25 40 80 Not bright-dipped 16 29 27 -25 Bright-dipped 30 32 32 The pyronine caused the bath to become deep red in color, and during electrolysis of the bath there was some foaming presumably caused by the pyronine. Pyronine was also used in a bath of similar composition at a concentration of two grams per liter with excellent results.

A bath similar to that above described was made employing five grams per liter of pyronine but omitting the molybdenum. The following results were obtained:

Current density 7 25 40 Not bright-dipped 13 12 12 13 Bright-dipped 26 29 29 27 I Emmple 40 A cyanide-zinc plating bath similar to that of the preceding example but containing as a metal brightener a compound of group VI sub-group 1 was made up as follows:

Grams per liter Zinc oxide (ZnO) 45 Sodium hydroxide (NaOH) 38 Sodium cyanide (NaCN) Tungsten trioxide (W03) 5 Pyronine 2 The tungsten trioxide corresponds to about four grams per liter of tungsten. The deposits obing bath made up with:

\ tained employing this bath were not quite as good as those of the preceding example, largely, I believe, by reason of the smaller efllcacy of tungsten as a brightener. At a current density of about seven amperes per square foot, an unbright.-dipped deposit gave a reflectometer reading of about sixteen, and a bright-dipped deposit made at the same current density gave a reading of about thirty one.

Example 41 A cyanide-zinc bath using a metal of group VI sub-group land a. metal of group VIII series 4 as well as an oxyheterocyclic compound, was made up asfollows: U

Grams per liter Zinc oxide (ZnO) 45 Sodium hydroxide (NaOH) 38 Sodium cyanide (NaCN) Molybdenum trioxide (M003) 2 Cobalt sulfate (C0SO4-7H2O) 1 Pyronine 2 The molybdenum trioxide corresponds to about one and three-tenths grams per liter of molybdenum and the cobalt sulfate corresponds to about twenty-one hundredths of a gram per liter of cobalt. Zinc deposits made employing this bath were of good character. Deposits made at a current density of about twenty-five amperes per square foot gave a reflectometer reading without bright-dipping of about twenty-four, and bright-dipped, a reading of thirty-sthree.

Example 42 A cyanide-zinc plating bath was made up with:

, Grams per liter Cobalt sulfate (COSO4'7H20) 8 Pyronine 5 I The following results were obtainedt Current density '7 25 40 80 Not bright-dipped '11 21 21 10 Bright-dipped 26 33 30 26 Example 43 Another furfural derivative characterized by the presence of an oxyheterocyclic ring of four carbon atoms and one oxygen atom, furfuryl alcohol, was used in conjunction with a metal of group VI sub-group 1 in a cyanide-zinc, plat- Grams per liter Molybdenum trioxide (M003) 8 Furfuryl alonhnl 5 The bath was deep red in color. A number of polished. copper sheets and a number of commercial steel articles were plated employingthis bath. Deposits made on polished copper sheets gave the following results at the indicated current densities:

Current density l 25 40 80 Not bright-dipped 15 28 27 2 Bright-dipped 25 33 32 2 The bath of this example was studied over a considerable period of time and, unlike baths containing furfural, the bath of this example appeared to be quite stable.

A bath similar to that of this example was made up employing furfuryl alcohol but omitting the molybdenum. The following results were obtained:

Current density -i *1 2s 40 so Not bright-dipped 16 3 1 1 Bright-dipped 31 9 3 2 Example 44 A cyanide-zinc plating bath was made up with:

Grams per liter Potassium ferrocyanide (K4F6(CN)6'3H2\Q).. 12

Furfuryl alcohol 5 A number of zinc deposits made at the below-indicated current densities gave the following results:

Current density 7 25 80 Not bright-dipped. 14 15 20 21 Bright-dipped 25 26 28 30 It is to be observed that deposits employing iron as a metal brightener tend to have a superficial colored film. While the plates sometimes appear quite bright when visually observed, the reflectometer readings of the unbright-dipped plates are much lower than would be expected.

Example A cyanide-zinc plating bath was made up with:

' Grams per liter Titanyl sulfate (TiOSOi) 0.5 Furfuryl-a 5.0

The following results were obtained:

Current density Not bright-dipped.-.- 11 13 i7 20 Bright-dipped l 23 26 31 32 Example- 46 v A cyanide-zinc bath employing still another 7 oxyheterocyclic compound which is a furfural derivative characterized by the presence of an oxyheterocyclic ring of four carbon atoms and one oxygen atom, tetrahydrofurfuryl alcohol, was made up with: 4

Grams per liter Molybdenum trioxide (M003) 8 Tetrahydrofurfuryl alcohol 8 At a current density of about twenty-five amperes per square foot, quite bright deposits were obtained. At this current density, unbrightdipped deposits gave a reflectometer reading of about thirty, and bright-dipped deposits thirtyeight.

A cyanide-zinc bath was made up using eight.

grams per liter of tetrahydrofurfuryl alcohol but omitting molybdenum. The following results were obtained:

Current density '1 25 40 so Not bright-dipped 13 19 11 8 Bright-dipped 28 29 34 26 Ezample 47 A cyanide-zinc plating bath was made up with:

k Grams per liter Chromium sulfate '(Cr(SO4):-I5H2O) 4 Tetrahydrofurfuryl alcohol 7 Employing this bath, very go d deposits were obtained when compared with other deposits resulting from the use of chromium as a brightener.

Deposits made on polished copper plates gave the following results at the indicated current densities:

Currentdensity '1 25 4o '30 Not bright-dipped 24 23 24' 25 Bright-dipped 1- 30 2a 27 27 This bath displayed a quite bright range at rela- Erample 48 v A cyanide-zinc plating bathwasmade up as follows:

Grams per liter 5 Cobalt sulfate (CoSO4-7Hn0) 8 Tetrahydrofurfuryl alcohol 7 The following results were obtained:

Current density 7 25 40 1 Not bright-dipped 11 2o 29 30 Bright-dipped 21 31 35 I 36 Example 49 Euroin is another example of an oxyheterocyclic compound which may be considered as a 15 furfural derivative and which is characterized by the presence of an oxyheterocyclic ring of four carbon atoms and one oxygen atom. A cyanide-zinc plating bath was made up with:

- Grams per liter Molybdenum trioxide (M003) 8 Furoin 5 A number of zinc deposits were made employing I the bath .of 'this example and, at the indicated 25 2 current densities, the following results were obtained on polished copper sheets:

Current density 7 25 40 so Not bright-dipped 17 27 28 26 3 Bright-dipped 26 33 32 32 The furoin colored the bath a deepred. It is also to be noted that after the bath was several days old it did not give a good results. Apparently furoin deteriorates in the bath, tho not 35 nearly so quickly as does furfural.

A bath was made up employing five grams per liter of furoin as above but omitting molybdenum. The following results were obtained:

Current density a '25 40 so 40 Not bright-dipped 16 16 1 1 Bright-dipped 32 32 3 1 Example 50 A cyanide-zinc plating bath was. made up with: 45

. Grams per liter Manganese sulfate (Mnsowimo) 1 Furoin 5 tlvely low current densities. Zinc deposits obtained using this bath gave the following reflecfiimeter readings at the indicated currentdensi- 1 es:

Current density 7 25 40 80 Not bright-dipped 19 31 21 2 Bright-dipped 27 35 30 2' Example 51 A cyanide-zinc plating bath was made up with} Grams per liter Potassium ferrocyanide (K4Fe(CN)s-3HaO) 12 Furoin 5 75 Deposits made from the bath of this example were much influenced by bright-dipping as is customary with deposits obtained from baths containing iron as a brightener. The following results were obtained with deposits made at the indicated current densities:

Current density 'l 40 80 Not bright-dipped 16 15 24 24 Bright-dipped 32 27 33 Example 5 3 A cyanide-zinc plating bath was made up with:

. Grams per liter Titanyl sulfate (TiOSO4) 1 Furoin 5 The following results were obtained using this bath:

Current density 7 25 40 80 Notbright-dipped 13 16 26 22 Bright-dipped 30 27 29 Example 54 Hydrofurfuramide is still another oxyheterocyclic compound which may be considered as a furfural derivative, and it is characterized by the presence of an oxyheterocyclic ring of four carbon atoms and one oxygen atom. Employing this compound, a bath was made up with:

. Grams per liter Molybednum trioxide (M003) 8 Hydrofurfuramide s 5 Using this bath to make specimen-zinc deposits on polished-copper sheets, the following results were obtained at the indicated current densities:

Current density. 'l 25 80 Not bright-dipped 16 25 2'7 21 Bright-dipped 27 36 34 29 The bath was colored a dark red by the hydrofurfuramide.

Similar baths were also made up employing various other amounts of hydrofurfuramide and at one gram per liter, for instance, deposits only slightly less brilliant were obtained.

A cyanide-zinc plating bath was also made up wit five grams per liter of hydrofurfuramide omitting the molybdenum. With this bath the following results were obtained:

Current density '7 25 40 80 Not bright-dipped 16 8 1 1 Bright-dipped 32 19 4 2 Example Furoic acid is another furfural derivative characterized by the presence of an oxyheterocyclic ring of four carbon atoms and one oxygen atom. Employing this compound, a cyanide-zinc plating bath was made up with:

- Grams per liter Molybdenum trioxide (M003) 8 Furolc acid 8 Deposits produced employing this bath were considerably poorer than the deposits obtained by the bath of the preceding example. The furoic acid, however, effected a considerable improvement in the character of the deposit. The baths of this example were studied for a considerable period of time and were found to be stable.

Example 56 A cyanide-zinc plating bath employing the oxyheterocyclic compound paraldol was made up with: V

Grams per liter Molybdenum trioxide (M003) 8 Paraldol 5 The paraldol was not as pure as that used in some of the subsequent examples and considerable difiiculty was encountered in dissolving it. The paraldol was added in alcohol solution. Specimen plates made using this bath gave the following results:

Current density 'l 25 40 80 Not bright-dipped 14 24 30 28 Bright-dipped 21 29 38 33 A bath similar to that given above was made up employing five grams per liter of paraldol but omitting molybdenum. Zinc deposits made on polished copper sheets at the indicated current densities gave the following results:

The paraldol used in this example was much purer than that of Example 56, and it dissolved readily without the use of alcohol. Employing this bath, specimen zinc plates were made up and the following refiectometer readings obtained:

Current density 7 25 40 80 Not bright-dipped 33 32 21 42 Bright-dipped 34 30 21 36 As is usual with deposits made from baths containing nickel as an addition agent, the deposits obtained were not greatly benefited by the use of a bright-dip.

Example 58 A cyanide-zinc plating bath was made up with:

Grains per liter Chromium sulfate (Cr(SO4)a-15H2O) 4 Paraldnl 5 The paraldol used was the .purer paraldol referred to in Example 5'7. The following results were obtained:

Current density '1 25 40 so Not bright-dipped 23 21 2a 29 Bright-dipped so so 33 33 Example 59 Ethyl furoate is an oxyheterocyclic compound which may be regarded as a derivative of furfural. Like furfural, it contains'an oxyheterocyclic ring of four carbon atoms and one oxygen atom. Employing this compound a bath was made up with:

Grams per liter Molybdenum trioxide (M003) 8 Ethyl furoate 3 The bath was colored red by the organic compound. Using the bath to plate a number of zinc specimens, the following results were obtained at the indicated current densities:

Current density 40 80 Not bright-dipped 22 32 Bright-dipped 35 37 A cyanide-zinc plating bath was also made up with three grams per liter of ethyl furoate but omitting the metal brightener. The following results were obtained:

' Current density 'l 25 40 80 Not bright-dipped. 10 13 9 9 Bright-dipped 23 31 28 28 The methyl furoate not entirely soluble in Example 60 Methyl furoate is an oxyheterocyclic compound very similar to the one of the preceding example. A cyanide-zinc plating bath was made up with:

: Grams per liter Molybdenum trioxide (M002) 8 Methyl 'furoa 5 The inclusion of methyl furoate in the bath caused it to become dark brown in color, and it is probable that the methyl furoate reacted with some constituent in the bath to form a detrimental product. However, when the bath was freshly made up, fairly good deposits were obtained as below indicated:

Current density '1 '25 Not bright-dipped... so 25 Bright-dipped s5 32 A similar bath was made up but omitting the molybdenum, the following results being obtained:

Current density 7 25 40 Not bright-dipped 13 12 10 8 Bright-dipped 31 29 25 23 Example 61 A cyanide-zinc plating bath was made up with:

Grams per liter nickel sulfate (mango) 05 Methyl furoate 5.

the bath. and some of the organic material remained undissolved. Surprisingly excellent resuits were obtained with the combination of this example. Specimen plates were made at the below indicated current densities:

Current density; '1 25 40 so,

Not bright-dippedunne 37 37 37 26 Bright-dipped 28 30 33 8 Example 62 A cyanide-zinc plating bath was made up with:

Grams per liter Aluminum sulfate (AI2(SO)4)2) 12 Methyl furoate '5 This bath gave unexpectedly good results tho the methyl furoate did not behave as well as in the preceding example. Specimen deposits gave the following reflectometer reading at the indicated current densities:

Current, density '1 25 40 so Not bright-dipped 9 2o 21 2o Bright-dipped 22 so 32 3o Example 63 Another oxyheterocyclic compound which may be considered a derivative of furfural is furfurylamine. This compound, like iurfural, is characterized by the presence of an oxyheierocyclic ring made up with four carbon atoms and one oxygen atom. A cyanide-zinc plating bath was made up with: I

Grams per liter Molybdenum trioxide (M002) 8 Furfllrylamine 5 The furfurylamine seemed to react with some constituent'of the bath, tho so far as could be determined this action was not detrimental. The bath, however, did not give as good results as might be expected. The following results were obtained:

Current density 25 40 Not bright-dipped. 21 2'7 Bright-dipped 34- 35 A cyanide-zinc bath was also made up as above with five grams per liter of furfurylamine .but

omitting the metal brightener. Specimens plated in this bath gave the following reflectometer readings at the indicated current densities:

Current .density.. e 25 40 80 Not bright-dipped 10 11 10 8 Bright-dipped 2s 2s 2a 22 ampl I Cram: per liter Molybdenum trioxide (M002) s Furfuramide 3 Anumberofspecimenplatesweremadeusing,

this bath. and the 1011071118 Milt: obtained:

Current density '1 25 40 so Not bright-dipped 19 2s 29 24 Bright-dipped 29 s4 35 29 The bath gave good-deposits when" it was first made, but upon standing it apparently deteriorated. The deterioration was not-as rapid nor as complete as was the case with furfural, however.v

A similar bath was made up employing furfuramide but omitting molybdenum. with this bath the following results were obtained:

Current density 7 25 4o 80 Not bright-dipped 16 18 5 2 Bright-dipped 30 v 31 17 12 Example 65 A cyanide-zinc plating bath was made with:

Grams per liter Chromium sulfate (CI(SO4)s-15H:O) 4

Fin'i'uramide 3 It is observed that baths containing furfuramide are red in color. Zinc depodts were made on a number of polished copper sheets and the following reflectometer readings obtained at the indicated current densities:

Current density 7' 25 40 80 Not bright-dipped 20 18 v23 26 Bright-dipped, 33 '29 29 '25 Example 66 A cyanide-zinc plating bath was made up with:

Grams per liter Titanyl sulfate (T1OSO4) 0.5 Furfuramide 3 Deposits of uniform appearance were obtained, but they were not unusually bright. At a current density of about forty amperes per square foot an unbright-dipped plate gave a reflectometer reading of twenty one, and a bright-dipped plate gave a reading of twenty seven.

Example 67 Tetrahydrofurfurylamine is another furfural, derivative characterized by the presence of an oxyheterocyclic ring of four carbon atoms and one oxygen atom. A cyanide-zinc plating bath was made up with:

- Grams per liter 7 Molybdenum trioxide (M003) 8 Tetrahydrofurfurylamine 5 A precipitate formed upon standing, and it appears that the organic addition agent of this example is not entirely stable. Zinc deposits were made using this bath with the following results:

Current density 7 40 80 Not bright-dipped 14 18 24 18 Bright-dipped 26 29 33 33 A similar cyanide-zinc plating bath was made up with five grams per liter of tetrahydrofurfurylamin'e but omitting the molybdenum. A number of zinc deposits were made employing this bath and the following reflectometer readings were obtained at the indicated current densities:

Current density 7 25 40 80 Not bright-dipped 16 14 16 13 Bg-ight-dipped 29 28 28 29 Example 68 A cyanide-zinc plating bath was made up with:

Gra'ms per liter Molybdenum trioxide (M003) 8 Dihydroxymethylxanthene 5 The oxyheterocyclic compound caused the bath to become red in color, and foaming was caused during electrolysis. Using this bath, the following results were obtained:

Current density 7 25 40 80 Not bright-dipped 13 17 27 31 Bright-dipped 24 28 35 35 A similar cyanide-zinc plating bath was niade up employing the same amount of dihydroxymethylxanthene but omitting the molybdenum. A number of zinc deposits were made employing this bath with the following results:

Current density '7 25 40 80 Not bright-dipped 13 14 20 20 Bright-dipped 19 25 3O 36 Example 69 l A cyanide-zinc plating bath was made up with:

Grams per liter Chromium sulfate (Cr(SO4)3-15mO) 4 Dihydroxymethylxanthene 5 A number of specimens were electrodeposited on polished copper sheets, and reflectometer readings obtained 'at the indicated current densities as follows:

A cyanide-zinc plating bath was made up with: Grams per liter *Aluminum sulfate (A12(S O4)3) 12 Dihydroxymethylxanthene 5 Zinc specimens plated employing this bath gave the following results:

Current density '1 25 40 80 Not bright-dipped '15 17 19 21 Bright-dipped -1 27 31;

Example 72.

A cyanide-zinc plating bath was made up with:

Grams per liter Molybdenum trioxide (M003) 8 Fluores 5 The bath of this example exhibited the fluores-. cence which would be expected, and there was a centain amount of foaming during electrolysis. Zinc deposits produced from this bath gave the following 'reflectometer readings at the indicated current densities:

Current density 7 25 40 80 Not bright-dipped 16 25 27 23 Bright-dipped 28 34 36 31 A similar cyanide-zinc plating bath was made up employing five grams per liter of fluorescin but omitting the metal brightener. The following results were obtained:

Current density 7 25 40 80 Not bright-diped 18 9 10 7 Bright-dipped 30 28 26 I 18 Example 73 A cyanide-zinc plating bath was made up with Grams per liter Nickel ammonium sulfate (NiSO4 (NH4) 2S O4-6H2O) 1 Fluores in 5 Zinc deposits produced using this ba'th gavev the following reflectometer readings at the indicated current densities:

Current density 'z '25 40 a0 Not: bright-dipped 35 31 28 20 Bright-dipped 32 30 23 17 As is customary with baths employing nickel as an organic brightener, the deposits are of better character before bright-dipping than they are after bright-dipping.

Example 74 A cyanide-zinc plating bath was made up with: Grams per liter Molybdenum trioxide (M002) 8 Morpholine Employing this bath, zinc deposits were made up and the following results obtained:

current density 7 25 40 so Not bright-dipped 1o 19 27 29 Bright-dipped 24 31 a4 31 A similar cyanide-zinc bath was made up using morpholine but omitting the molybdenum. With this bath the following reflectometer readings were obtained with zinc deposits made at the indicated current densities:

Current density 7 25 40 80 Not bright-dipped 11 13 Bright-dipped 26 28 30 28 Example 75 p A cyanide-zinc plating bath was made up with:

Grams per liter Molybdenum trioxide (M003) 8 Morpholine etha 5 Employing this bath, the following results. were obtained:

Current density 7 40 so Not bright-dipped. 10 22 2a 27 Bright-dipped 28 32 35 34 A similar cyanide-zinc plating bath was made up using morpholine ethanol but omitting the molybdenum with the following results:

Current density "l 25 40 80 Not bright-dipped 11 '7 8 6 Bright-dipped 26 31 32 Example 76 A cyanide-zinc plating bath was made up using:

' Grams perliter Potassium ferrocyanide (K4Fe(CN)s'3H20) 12 Morpholine ethanol 5 As is usual with baths containing iron as 'a brightener, there is a slight film on the deposit which seems to prevent the reflectometer readings being as high as would be expected from a visual observation. Zinc specimens plated in the bath of this example gave the following reflectometer readings at the indicated current densities:

Current density 7 25 40 80 Not bright-dipped. 13 18 20 17 Bright-dipped 27 32 33 31 Example 7 7 A cyanide-zinc plating bath was made up with:

Grams per liter Phenylmorpholine hydrochloride 0.5 It is observed that larger amounts of the phenylmorpholine hydrochloride were not soluble in the bath. Employing this bath. cyanide-zinc deposits were made and the following reflectometer readings obtained at the indicated current densities:

Current density 7 25 40 so Not bright-dipped 1c 19 2s 31 Bright-dippednn; s4 31 a4 A similar cyanide-zinc plating bath was made up employing the organic addition agent but omitting the metal brightener. Zinc deposits obtained from this bath gave the following reflectometer readings at the indicated current densities:

Current density 'l 25 80 Not bright-dipped 1'7 10 4 4 Bright-dipped 34 '30 25 15 Example 79 'A cyanide-zinc plating bath was made up'wit-h:

' Grams per liter Cobalt sulfate (CoSOflmO) 8 Phenylmorpholine hydrochloride 0.5 The following results were obtained:

Current density 'l 25 40 80 Not bright-dipped 19 29 28 26' Bright-dipped 29 33' 37 35 Example 80 An oxyheterocyclic compound similar to that of the preceding example was used in a cyanide-zizic plating hath made up with:

- Grams per liter Molybdenum trioxide (M003) 8 Butylmorpholine hydrochlorlde 5 Deposits made from this bath were examined using the reflectomete'r, and the following results were obtained at the indicated current densities:

Current density 7 25 40 80 Not bright-dipped 12 17 27 30 Bright-dipped 24 27 '34 36 A similar cyanide-zinc plating bath was made up employing the organic addition agent but omitting the molybdenum. The following results were obtained:

Current density 'l 25 40 80 Not bright-dipped 11 7 2 2 Bright-dipped 31 26 21 13 Example 81 Acyanide-zinc plating bath was made up with:

, Grams per liter Molybdenum trioxide (M002) 8 Diphenylene oxide The diphenylene oxide was very diflicultly soluble, and it is probable that somewhat less than the one-half gram per liter used dissolved in the bath. Employing the bath of this example, zinc deposits were made and examined under the reflectometer with the following results:

Current density 'l 25 40 Not bright-dipped 17 27 29 28 Bright-dipped 26 32 34 35 A similar cyanide Zinc plating bath was made up employing diphenylene oxide but omitting the molybdenum with the following results:

Current density) 'l 25 '40 80 4 Not bright-dipped. i5 13 9 9 Bright-dipped... 30 28 26 27 Example 82 acid was included in a cyanide-zinc plating bath A cyanide-zinc plating bath was made up with: made up with Grams per liter Grams per liter Molybdenum trioxide (M003) a Molybdenum trioxide (M003) a Coumalic acid 3 Cyclohexene oxide" 3 While three grams per liter of cyclohexene oxide wereadded, probably not more than one gram per liter was actually dissolved. The remainder formed an oily film on the surface of the bath. During electrolysis the film became dark brown in color. The following results were obtained when the bath was used to plate specimen zinc deposits on polished copper sheets:

Current density 'z 25 40 so Not bright-dipped. 9 21 28 24 Bright-dipped"; 25 32 so A similarbath was made up'omitting molybdenum and the following results were obtained:

Current density 7 25 80 Not bright-dipped 10 I 9 11 12 Bright-dipped 26 22 26 28 Example 83 A cyanide-zinc plating bath was made up including:

' Grams per liter Nickel sulfate (NlSOr'lI-IaO) 0.5 Cyclohexene oxide 3.

The following results were obtained:

Current density 7 25 40 80 Not bright-dipped 21 28 20 24 Bright-dipped 30 29 20 30 Example 84 A cyanide-zinc plating bath was made up with:

\ Grams per liter Molybdenum trioxide (M003) 8 Glycol formal 5 Zinc deposits made employing this bath gave the following readings using the reflectometer at the indicated current densities:

Current density; 7 25 40 so Not bright-dipped 10 23 31 30 Bright-dipped 25 33 35 34 A similar cyanide-zinc plating bath was made up using glycol formal but omitting molybdenum, and the following results were obtained:

remain in the bath as such, it being probable that the compound polymerizes. At a current density of about seven amperes per square foot an unbright-dipped zine deposit gave a reflectometer reading of thirty, and a bright-dipped deposit a reading of twenty three.

5 Example 86 Coumalic acid, an oxyheterocyclic compound also known as 2-keto-1,2-pyran-5-carboxylic It is observed that coumallc acid is probably not stable in the bath as it hydrolyzes very readily.

' Zinc deposits made using this bath gave the following results at the indicated current densities:

Current density '7 25 40 80 Not bright-dipped. 12 25 30 2'7 Bright-dipped 30 33 36 34 Current density 7 25 40 80 Not bright-dipped 10 8 8 8 Bright-dipped 24 29 33 28 Example 87 Kojic acid, an oxyheterocyclic compound, also known as S- hydroXy-gamma-pyrone, was included in a cyanide-zinc plating bath made up with:

. Grams per liter Molybdenum trioxide (M003) 8. Kojic acid -1 3.3

At a current density of about twenty-five amperes per square foot an unbright-dipped zinc deposit obtained using this bath gave a reflectometer reading of twenty-five, and a brightdipped deposit gave a reading of thirty-five. Kojic acid alone was used as an addition to a cyanide-zinc plating bath with the following results:

Current denslty 1 7 25 40 at Not bright-dipped 17 2s 22 so Bright-dipped 21 29 29 29 Example 88 A cyanide-zinc plating bath was made up with:

Grams per liter Molybdenum trioxide (M003) 8 Phthalide 5 When the bath was freshly made up, deposits made at a current density of about forty amperes per square foot gave, before bright-dipping, a reflectometer reading of twenty-three, and, after bright-dipping, a reading of thirty-five. It appears that phthalide is not stable in the bath because upon standing a dark precipitate formed.

Example 89 I 1 A cyanide-zinc plating bath was made up with:

' Grams per liter Nickel sulfate (NiSO4-7H2O) 0.5 Phtha'lidp 5.

A number of copper plates were zinc coated at the below indicated current densities with the following results:

Current density 7 25 40 80 Not bright-dipped 31 28 24 9 Bright-dipped 31 28 24 10 A cyanide-zinc plating bath was made up using five grams per liter of phthalide but omitting the nickel. With this bath the following results were obtained: 'Current density 7 25 40 80 Not bright-dipped 12 8 11 10 Bright-dipped 31' 28 29 28- Molylbdenum trioxide (M001) 8 Thioxane The organic compound was quite insoluble, and it floated upon the bath in small droplets. A slight precipitate formed after the bath was allowed to stand. Employing this bath, the following results were obtained at the indicated current densities: I Current density 7 25 40 80 Not bright-dipped 11 18 23 27 Bright-dipped 28 30 33 33 A similar bath was made up using thioxane but omitting the metal brightener. Zinc deposits made at the indicated current densities gave the following results:

Current density 7 25 40 80 Not bright-dipped 16 9 10 10 Bright-dipped 27 25 25 22 Example 91 A cyanide-zinc plating bath was made up with:

Grams per liter Molybdenum trioxide (M003) 8 Formvar 1 This oxyheterocyclic addition compound was quite insoluble in the bath, but it appears that some slight amount at least was dissolved. The following results were obtained: Current density '1 25 40 so Not bright-dipped 12 25 29 29 Bright-dipped 26 32 34 34 A bath was also made up using formvar but omitting the metal brightener with the following results:

Current density 7 25 40 80 Not bright-dipped .12 10 13 13 Bright-dipped 22 25 29 29 Example 92 I A cyanide-zinc plating bath was made up with:

Grams per liter Molybdenum trioxide (M003) 8 Phthalidylphenylsulfide 5 With this combination of an oxyheterocyclic compound and metal brightener, the following results were obtained: Current density 7 25 40 so Not bright-dipped 15 21 27 27 Bright-dipped 33 29 35 35 A bath was also made up as above but omitting the molybdenum with the following results:

Current density "1 25 40 so Not bright-dipped 8 8 5 5 Bright-dipped 27 27 23 22 Example 93 A cyanide-zinc plating bath was made up with:

. Grams per,liter Molybdenum trioxide (MoOa) 8 Rotenone 1 Errample so A cyanide-zinc plating bath was made up with: Grams per liter The organic compound was almost entirely insoluble in the bath, somewhat less than one gram per liter being actually dissolved. Durin electrolysis of the bath, the addition agent caused some foaming, particularly at higher current densities. A number of zinc deposits were made using this bath, and the specimen plates examined using the reflectometer. The following results were obtained:

Current density 'z 25 40 so Not lorlght-dipped 11 17 27 14 Bright-dipped 32 26 33 32 A cyanide-zinc plating bath similar above, using on gram per liter of rotenone but omitting the molybdenum, was made up. The

following results were obtained:

Current density '7 25 40 80 Not bright-dipped 6 10 18 18 Bright-dipped 21 22 31 33 to the one bath constituents may readily be determined for each particular instance by a few trials.

The metals of group VI sub-group 1 may be used in widely varying amounts, the upper limit on the quantity being largely determined by economic considerations. In view of the high cost of the metals of this group, it would not at the present time be commercially feasible to employ them in large quantities. More specifically, the metals of group VI sub-group 1' should be used in amounts not substantially less than about one hundredth of a gram per liter, and no more than about forty grams per liter can economically be used.

Molybdenum is the best metal of this group and it is, in fact, by far the best of the brightening metals. I generally prefer to use from about twenty-five hundredths of a gram to twentyfive grams per liter of molybdenum. More specifically, it is preferred to use from about one to twelve grams per liter of molybdenum. It will be understood that while reference is made to the amount of metal used, the metal is present in the bath in the form of a soluble compound.

' The metals of group VII sub-group 1 should also be employed in substantial amounts. It is generally desirable to use no less than about five-thousa'ndths of a gram per liter and not substantially more than about fifteen grams per liter. Manganese is preferably usedin amounts between about one and five grams per liter, while, more specifically, about one to three grams per liter should be used.

The metals of group VIII series 4, similarly, should be used in substantial amounts as soluble compounds such as potassium. ferrocyanide, co-

bait sulfate, cobalt chloride, cobalt oxide, nickel sulfate, nickel chloride, and nickel oxide. Generally a soluble compound equivalent to no less than about five-hundredths of a gram per liter of one of these metals should be used. a

When titanium is employed as a brightening metal, an amount equivalent to about one-half gram per liter of titanyl sulfate should be used, tho, of course, larger or smaller amounts may be employed if desired.

While the amount of aluminum used as a brightening metal may be greatly varied, it is generally desirable to employ an amount of aluminum equivalent to about five to twelve grams per liter of aluminum sulfate.

While an attempt has been made above to outline, roughly, some of the considerations involved in selecting the quantities of metal brighteners, it will be understood that in a particular instance the requirements may most readily be determined by a few simple trials.

Each of the brightening metals has characteristics peculiar to itself, and the selection of a metal brightener for a particular bath may be infiuenced by the characteristics desired. While, generally speaking, I may employ any metal brightener in conjunction with organic addition agents, it is preferred to use a metal from the group consisting of molybdenum, chromium, cobalt, manganese, nickel, iron, titanium, rhenium, aluminum, and tungsten.

Molybdenum is by far the best of the brightening metals as has been'pointed out above, the occasionally some other brightening metal will give comparable results in a particular combination.

Chromium is very satisfactory as a brightening metal, but it has the fault of vhydrolyzing in the bath and precipitating out. This characteristic of chromium brighteners makes their use too expensive for most purposes.

Cobalt and nickel both have the fault of accelerating anode corrosion tho nickel is a much worse offender than cobalt. When cobalt is used as a metal brightener the deposits appear a little white, and the refiectometer readings are lower than one would expect from visual observation.

In many combinations nickel produces quite satisfactory deposits but the deposits should not be bright-dipped. Deposits produced from baths containing nickel as a brightener darken when bright-dipped tho they still appear bright to the eye.

When manganese or tungsten are used as brightening metals, the deposits have a brownish film. Despite the fact that many deposits of pleasing and brilliant appearance are obtained using these metals, the deposits almost uniformly give much lower refiectometer readings than would be expected from visual observation. The brownish film is removed when the deposits are bright-dipped.

Iron, like manganese and tungsten, causes the formation of a slight film on the deposit. This film also lowers the refiectometer readings without making the plates appear correspondingly dull to the eye. The film, however, is removed by bright-dipping.

Titanium occasionally causes the formation of a slight gray film which greatly lowers the reflectometer readings. The gray film is not ordinarily removed by bright-dipping the deposit.

When aluminum is used as a metal brightener the deposits ordinarily have a whitish appearance, and while the deposits are very pleasing and bright when visually observed, the refiectometer readings are astonishingly low.

Bright-dipping does not entirely change the whitish appearance of the deposit.

Rhenium is quite excellent as a brightening metal, but it is so rare atthe present time that its commercial application would be impractical. Should the metal become less expensive, it could be used very satisfactorily as a brightener.

While my invention is particularly directed to the cooperative use of organic addition agents and metal brighteners, it will be understood that oxyheterocyclic compounds are somewhat eflicacious apart from metal brighteners and that it may sometimes be found desirable to use them alone. p

While, as has been noted above, I may employ any oxyheterocyclic compound, it will be understood that the compound should retain its oxy heterocyclic structure in cyanide-zinc plating baths and, of course, the compound should be to some extent soluble in the bath. If an oxyheterocyclic compound is not readily soluble, it may be more satisfactorily dissolved by adding it in a solvent such as alcohol or acetone.

While I may employ any oxyheterocyclic compound with or without a metal brightener, it is preferred to employ an oxyheterocyclic compound from the group consisting of piperonal, piperonyl alcohol, piperonylic acid, piperine, safrole, piperonal acetophenone, coumarin, furfural, furfuran, pyronine, tetrahydrofurfuryl alcohol, hydrofurfuramide, paraldol, ethyl furoate, methyl furoate, furfural amine, tetrahydrofurfuralamine, dihydroxymethylxanthene, fluorescein, morpholine ethanol, phenyl morpholine hydrochloride, butyl morpholine hydrochloride, diphenylene oxide, cyclohexene oxide, glycol formahcoumalic acid, and furfuramide.

The oxyheterocyclic compounds are preferably employed in about the amounts given in the above examples. It will be understood that the quantity used in the examples was determined in each instance by trying. the organic addition agent at widely varying concentrations until about an optimum was found. If it is desired to employ a particularoxyheterocyclic compound in a still different. specific instance, the amount to be used may readily be determined by a few simple tests.

The brightness figures given in the above examples refer, of course, to the number of micro- .amperes read on the micro-ammeter III of the refiectometer. The figures are therefore specific to the apparatus used for the determinations. In view of the fact that the current developed by the photoelectric cell is directly proportional to the light it receives, and in view of the method of standardizing the instrument, the data can be given an absolute significance by referring to a silver mirror. For example, a plate with a refiectometer reading of 38 microamperes is as bright as a polished silver mirror.

While I have shown a number of specific processes and cyanide-zinc baths in the foregoing, it will be understood that I do not intend to be limited thereto. Those skilled in the art may readily make numerous modifications of the discussed processes and baths without departing from the spirit of this invention.

This application is a continuation in part of my co-pending application Ser. No. 14,589, filed April 4, 1935 now Patent No. 2,080,520, and of my co-pending application Ser. No. 70,400, filed March v23, 1936 now abandoned.

I claim:

1. In a process for the electrodeposition of zinc, the step comprising depositing zinc from a cyanide-zinc bath in the presence of an oxyheterocycle compound.

In a process for the electrodeposition of zinc 

